The electronic structure and orientation of the surface methoxy species on Ni(111)

Photoelectron spectra of the methoxy species formed by the decomposition of methanol on nickel(111) indicate that the C-O-nickel bond is normal or nearly normal to the metal surface. This structural assignment for the adsorbate complex is consistent with new photoelectron data using linearly polarized synchrotron radiation.     

Solution of self-consistent field electronic structure equations by a pseudospectral method

A new method for solving self-consistent electronic structure equations which offers orders of magnitude reductions in computation time and storage space with no obvious loss of accuracy is described and applied to the restricted Hartree-Fock equations for the neon atom. Application to polyatomic molecules is straightforward both conceptually and numerically.     

The electronic structure of chlorine trifluoride: An approximate MO-LCAO-SCF calculation

Calculations have been performed on ClF₃ using an approximation scheme previously developed by the author. Only valence shell s and p orbitals are used in the basis. It is found that the T-shaped nuclear configuration can be satisfactory explained without the use of chlorine 3d orbitals. The calculated charge distribution is found to be similar to that postulated by the Gillespie and Nyholm model but with excess electronic charge on the fluorine atoms.

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Zusammenfassung Rechnungen am ClF₃ werden nach einem angenäherten SCF-Verfahren durchgeführt, wobei als Basis nur s- und p-Funktionen verwendet werden. Dabei zeigt sich, daß sich die T-Konfiguration des Moleküls auch ohne Einbeziehung von 3d-Zuständen des Chlors ergibt. Die erhaltene Ladungsverteilung entspricht der des Modells von Gillespie und Nyholm, jedoch mit größerer Elektronendichte am Fluor.

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Résumé ClF₃ a fait l'objet de calculs selon un schéma développé précédemment par l'auteur. La base ne contient que les orbitales s et p des couches de valence. La configuration nucléaire en forme de T peut être expliquée d'une maniére satisfaisante sans l'utilisation des orbitales 3d du chlore. La distribution de charge calculée est similaire á celle postulée dans le modéle de Gillespie et Nyholm avec cependant un excés de charge sur les atomes de fluor.

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This work was supported in part by the National Science Foundation and in part by Research Grant NsG-512 from the National Aeronautics and Space Administration.     

Two-photon photoemission study of the coverage-dependent electronic structure of chemisorbed alkali atoms on a Ag(111) surface

We report a systematic investigation of the electronic structure of chemisorbed alkali atoms (Li-Cs) on a Ag(111) surface by two-photon photoemission spectroscopy. Angle-resolved two-photon photoemission spectra are obtained for 0-0.1 monolayer coverage of alkali atoms. The interfacial electronic structure as a function of periodic properties and the coverage of alkali atoms is observed and interpreted assuming ionic adsorbate/substrate interaction. The energy of the alkali atom σ-resonance at the limit of zero coverage is primarily determined by the image charge interaction, whereas at finite alkali atom coverages, it follows the formation of a dipolar surface field. The coverage- and angle-dependent two-photon photoemission spectra provide information on the photoinduced charge-transfer excitation of adsorbates on metal surfaces. This work complements the previous work on alkali/Cu(111) chemisorption [Phys. Rev. B 2008, 78, 085419].     

On the importance of surface structure in electrochemistry: the well-defined Au (111) single crystal electrode surface

The electrochemical nucleation of cadmium onto vitreous carbon and onto tin oxide electrodes in studied using potentiostatic methods. The influence of supporting electrolyte is investigated and in every case new and interesting features arise. The deposition of cadmium on tin oxide is of particular interest and evidently occurs via an initial process of 2D nucleation followed, at higher overpotentials, by 3D nucleation.     

Surface electronic structure calculations using the MBJLDA potential: Application to Si(111)2 × 1

The Si(111)2 × 1 surface has been widely studied via a range of different experimental and theoretical techniques, and found to adopt a π‐bonded chain configuration. To determine an accurate electronic structure for this system, however, it has been found necessary to use sophisticated and very computationally expensive methods such as GW or hybrid functionals. In this article, we show that the MBJLDA approach, originally proposed by Tran and Blaha for bulk materials (Tran and Blaha, Phys. Rev. Lett. 2009, 102, 226401), yields results which are comparable to GW, and generally superior to those obtained from hybrid functional density functional theory calculations. The MBJLDA method is also substantially more computationally efficient. A procedure and justification for the application of the MBJLDA approach to surfaces in general is also provided. © 2014 Wiley Periodicals, Inc.     

The electronic structure of two forms of molecular ammonia adsorbed on Pt(111)

Two states of ammonia adsorbed on Pt(111) at 100 K are distinguished by photoemission, work function, and thermal desorption measurements. Ammonia at low coverages (θ ? $\text{1}\text{4}$), denoted α, orients as an inverted umbrella, bonds by transferring charge via its 3a₁ orbital, and increases its dipole moment to 2.0 D. High coverage β-NH₃ hydrogen-bonds to α-NH₃.     

Elongation method for electronic structure calculations of random DNA sequences

We applied ab initio order‐N elongation (ELG) method to calculate electronic structures of various deoxyribonucleic acid (DNA) models. We aim to test potential application of the method for building a database of DNA electronic structures. The ELG method mimics polymerization reactions on a computer and meets the requirements for linear scaling computational efficiency and high accuracy, even for huge systems. As a benchmark test, we applied the method for calculations of various types of random sequenced A‐ and B‐type DNA models with and without counterions. In each case, the ELG method maintained high accuracy with small errors in energy on the order of 10^?8 hartree/atom compared with conventional calculations. We demonstrate that the ELG method can provide valuable information such as stabilization energies and local densities of states for each DNA sequence. In addition, we discuss the “restarting” feature of the ELG method for constructing a database that exhaustively covers DNA species. © 2015 Wiley Periodicals, Inc.     

Calculating the SnS(010) surface electronic structure using the green function method

The electronic structure of the (010) surface in a layered SnS semiconductor terminating with Sn and S atomic planes is calculated by the Green function method. The electronic structure of a perfect crystal is calculated according to the linear combination of atomic orbitals (LCAO) using Slater s-, p-, and d-orbitals. Defect-induced changes in the density of states and the origin and orbital composition of electronic states in the band gap are discussed.     

The band structure of one-dimensional (tetrazaporphyrinato)cobalt(II). A semi-empirical self-consistent field crystal orbital analysis

The band structure of (tetraporphyrinato)cobalt(II) (2) has been investigated by means of a semi-empirical INDO (intermediate neglect of differential overlap) crystal orbital approach. The simplest stoichiometric unit of the title compound contains an uneven number of electrons. We have considered metallic and insulating (Mott) electronic distributions in the “half-filled” band. The Hartree-Fock energies for two spatial symmetries have been determined: (i) singly occupied Co 3d_z² band (a_1g) and (ii) singly occupied ligand-centered (a_1u) linear combination. The mean-field energies of insulating “Mott” states have been calculated by means of a grand canonical (GC) averaging procedure. The electronic ground state is of spatial A_1g symmetry (“half-filled” Co 3d_z² dispersion) and corresponds to an insulating band occupation. The calculated width of the a_1g dispersion amounts to 0.13 eV. It is argued that the band structure results of 2 are in qualitative agreement with available experimental results derived for (phthalocyaninato(cobalt(II).     

Some self-consistent perturbation calculations of 1J(CC)

Self-consistent perturbation calculations of 70 ¹J(CC) values are reported within the INDO framework. A least-squares agreement between the calculated and observed couplings, for a variety of bond multiplicities, provides values of 13.503 au^?6 and 5.072 au^?6 for (S_C²(O))² and 〈r^?3〉_C², respectively. The non-contact terms are found to be important in cases of multiple bonding.     

Bonding structure of phenylacetylene on hydrogen-terminated Si(111) and Si(100): surface photoelectron spectroscopy analysis and ab initio calculations

Interfaces between phenylacetylene (PA) monolayers and two silicon surfaces, Si(111) and Si(100), are probed by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and the results are analyzed using ab initio molecular orbital calculations. The monolayer systems are prepared via the surface hydrosilylation reaction between PA and hydrogen-terminated silicon surfaces. The following spectral features are obtained for both of the PA-Si(111) and PA-Si(100) systems: a broad π-π* shakeup peak at 292 eV (XPS), a broad first ionization peak at 3.8 eV (UPS), and a low-energy C 1s → π* resonance peak at 284.3 eV (NEXAFS). These findings are ascribed to a styrene-like π-conjugated molecular structure at the PA-Si interface by comparing the experimental data with theoretical analysis results. A conclusion is drawn that the vinyl group can keep its π-conjugation character on the hydrogen-terminated Si(100) [H:Si(100)] surface composed of the dihydride (SiH(2)) groups as well as on hydrogen-terminated Si(111) having the monohydride (SiH) group. The formation mechanism of the PA-Si(100) interface is investigated within cluster ab initio calculations, and the possible structure of the H:Si(100) surface is discussed based on available data.     

An efficient, fragment-based electronic structure method for molecular systems: self-consistent polarization with perturbative two-body exchange and dispersion

We report a fragment-based electronic structure method, intended for the study of clusters and molecular liquids, that incorporates electronic polarization (induction) in a self-consistent fashion but treats intermolecular exchange and dispersion interactions perturbatively, as post-self-consistent field corrections, using a form of pairwise symmetry-adapted perturbation theory. The computational cost of the method scales quadratically as a function of the number of fragments (monomers), but could be made to scale linearly by exploiting distance-dependent thresholds. Extensive benchmark calculations are reported using the S22 database of high-level ab initio binding energies for dimers, and we find that average errors can be reduced to <1 kcal/mol with a suitable choice of basis set. Comparison to ab initio benchmarks for water clusters as large as (H(2)O)(20) demonstrates that the method recovers ?90% of the binding energy in these systems, at a tiny fraction of the computational cost. As such, this approach represents a promising path toward accurate, systematically improvable, and parameter-free simulation of molecular liquids.     

Adsorption Behavior and Reaction Properties of NO and CO on Ir(111) and Rh(111)

Adsorption and reactions of NO over the clean and CO-preadsorbed Ir(111) and Rh(111) surfaces were investigated using infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD). Two NO adsorption states, indicative of hollow and atop sites, were present on Ir(111). Only NO adsorbed on hollow sites dissociated to N_a and O_a. The dissociated N_a desorbed as N₂ by recombination of N_a and by a disproportionation reaction between atop-NO and N_a. Preadsorbed CO inhibited atop-NO, whereas hollow-NO was not affected. Adsorbed CO reacted with O_a and desorbed as CO₂. NO adsorbed on the fcc-hollow, atop, and hcp-hollow sites in that order over Rh(111). The hcp-NO was inhibited by preadsorbed atop-CO, and fcc-NO and atop-NO were inhibited by CO preadsorbed on each type of the sites, indicating that NO and CO competitively adsorbed on Rh(111). From the Rh(111) surface-coadsorbed NO and CO, N₂ was produced by fcc-NO dissociation, and CO₂ was formed by reaction of adsorbed CO with O_a from dissociated fcc-NO.     

Ir spectroscopic and crystal morphology studies of the structure of alakli metal fluorophosphatozirconates (hafnates)

Potassium, rhubidium, and caesium fluorophosphatozirconates (hafnates) and oxo(hydroxo)fluorophosphatonitratometalates with PO ₄ ^3? /Zr molar ratios of 2.0, 1.5, 1.0, 0.66, 0.5, and 0.33 are synthesized for the first time. Most of them form either fine crystalline or X-ray amorphous particles. In order to characterize them IR spectroscopy and SEM are used. For the crystalline compounds the types of PO₄ groups and the character of bonds between fluorine and water are revealed. The occurrence of triple MeF₄·Rb(PO₄)_0.33·RbNO₃ (Me = Zr, Hf) salts and also M₃Me₃(PO₄)₅·3HF crystalline solvates is found. The layered habit of K₃Hf₃(PO₄)₅·3HF, RbHfF₂PO₄·0.5H₂O, Rb₃Hf₃(PO₄)₅·3HF, CsHfF₂PO₄·0.5H₂O, CsHf₂F₆PO₄·4H₂O, and CsH₂Hf₂F₂(PO₄)₃·2H₂O crystals gives grounds to suppose that the structure of these compounds is layered unlike the structure of triple MeF₄·Rb(PO₄)_0.33·RbNO₃ salts.     

Synthesis of PbSe nanocrystallites using a single-source method. The X-ray crystal structure of lead (II) diethyldiselenocarbamate

The compounds Pb{Se₂CN(C₂H₅)₂}₂ and Pb{Se₂CN(CH₃)(C₆H₁₃)}₂ were synthesised and characterised. The X-ray crystal structure of Pb{Se₂CN(C₂H₅)₂}₂ is reported. The use of these compounds as single-molecule precursors to produce PbSe by thermolysis in tri-n-octylphosphine oxide was investigated. The optical and morphological properties of the PbSe particulates were analysed; strong quantum confinement effects were observed in the optical spectra of nanodispersed PbSe in organic solvents.     

Ground state and phase transitions in a system of arg-cysteamines self-assembled on a Au(111) crystal surface

The translational and orientation order of arg-cysteamine molecules chemiabsorbed on the Au(111) crystal surface is considered. Couplings between carbon, nitrogen, and hydrogen atoms of the n-alkanethiols are approximated by the Lennard-Jones potential. Moreover, hydrogen bonds between oxygen and nitrogen and dipole-dipole interactions of the dipole moments of different atomic groups are taken into account. It is found that molecules are arranged in a 2 x 2 lattice and have the total symmetry C6 x Z2. The critical temperature of the phase transition to the tilted state Tc1, which breaks the symmetry C6, is estimated to be extremely high. The spontaneous breakdown of the remaining symmetry Z2 leads to the twisted state of the molecules and has the critical temperature Tc2=340 K.     

An efficient treatment of kinematic factors in pseudo-relativistic calculations of electronic structure

Relativistic two-electron operators obtained by the Douglas-Kroll transformation contain p-dependent kinematic prefactors which are not present in the corresponding Breit-Pauli operators. These factors are usually calculated using a resolution of the identity approach, which requires integral transformations. In the present article we describe an alternative approach, based on a local approximation, where the effect of the prefactors can be absorbed in the atomic contraction coefficients. The effect of the local approximation is investigated in detail. The suggested approach is simple to implement in integral codes that allow the use of a general contraction scheme. Received: 27 June 1997 / Accepted: 1 October 1997